The present invention relates to a radial plunger pump or radial plunger motor, comprising a rotor which can rotate about a stationary pintle, at least one radial cylinder bore being provided in the rotor, a plunger being arranged reciprocable in said bore, and the pintle being provided with an inlet duct and an outlet duct for supplying and discharging liquid to and from the cylinder bore.
In one frequently encountered design of a radial plunger pump, the rotor is made from bronze and the pintle is made from hardened free-cutting steel. When the pump is in operation, the pintle is subject to a considerable load which is directed substantially transversely to the pintle and emanates from the hydraulic pressure. Furthermore, the rotor usually rotates at a high speed about the pintle, so that there is a risk of considerable wear and, for this reason, in known plunger pumps it is chosen to combine a pintle made from hardened free-cutting steel and a rotor made from bronze.
As is known, in radial plunger pumps of this type there is a gap between the rotor and the pintle. Pressurized liquid leaks through this gap, a phenomenon which is known as leakage loss. In the known radial plunger pumps, it is usually the case that this leakage loss increases when the temperature rises, and consequently the efficiency of the pump falls. Also, bronze has a relatively low modulus of elasticity, so that the rotor is deformed under the influence of the hydraulic pressure in the gap between the pintle and the rotor, with the result that this gap becomes larger.
It is known to reduce the leakage loss from the abovementioned radial plunger pumps by making the rotor mainly from steel with an inner bronze bush which fits around the pintle. However, this is an expensive solution and does not give satisfactory results.
The object of the present invention is to eliminate the above drawback and to provide a radial plunger pump or radial plunger motor with a high level of efficiency.
The invention relates to a radial plunger machine comprising a pintle and a rotor which is rotatable about said pintle, at least one radial cylinder bore being provided in the rotor, a plunger being reciprocable arranged in said cylinder bore, and the pintle being provided with an inlet duct and an outlet duct for supplying and discharging liquid to and from the cylinder bore, respectively. According to the invention the pintle is made from a material with a higher coefficient of linear thermal expansion than the material of the rotor.
In the radial plunger machine according to the invention it is ensured that, when the temperature rises, the gap between the pintle and the rotor becomes smaller. This is highly advantageous since as a result it is possible to entirely or largely compensate for the fact that, when the temperature rises, the viscosity of the liquid falls, and can therefore pass through the gap more easily.
In a preferred embodiment of the radial plunger the pintle is made from stainless steel and has a higher coefficient of linear thermal expansion than the material of the rotor. Selecting stainless steel for the pintle in combination with a suitable material for the rotor, preferably free-cutting steel, has the considerable advantage that the coefficient of thermal expansion of stainless steel is high, in particular higher than most other grades of steel, such as in particular free-cutting steel. Consequently, in this case too it is possible to make the gap between the pintle and the rotor become smaller as the temperature rises.
In a particularly advantageous embodiment of the plunger pump or motor, the pintle is made from austenitic stainless steel. This specific grade of steel is suitable for absorbing the loads which act on the pintle over a prolonged period and, in particular, has an especially high coefficient of linear thermal expansion. In an advantageous embodiment thereof, the pintle made from austenitic stainless steel is subjected to a surface hardening treatment, which is of benefit in particular to the wear resistance of the pintle.
The invention also relates to a radial plunger machine comprising a rotor which is rotatable about a pintle, at least one radial cylinder bore being provided in the rotor, a plunger being reciprocable arranged in said bore, and the pintle being provided with an inlet duct and an outlet duct for supplying and discharging liquid to and from the cylinder bore, wherein the pintle is made from stainless steel.
It will be clear that the inventive idea can be applied to a radial plunjer pump and to a radial plunger machine which is used as a motor and which is supplied with pressurized liquid.